In comparison with a former MOS transistor, a MOS transistor (SJ-MOS transistor) of a super junction structure is known as an element for realizing low on-resistance (e.g., disclosed in JP-A-H09-266311). This SJ-MOS transistor is characterized in a repetitious pn column structure in a drift layer area. Plural methods are proposed to form this pn column. In these methods, a method for epitaxially growing the interior of a trench by LP-CVD after the trench is formed in a substrate is known as a method able to uniform a concentration distribution of a depth direction.
In trench filling using the general LP-CVD, a growth rate in an opening portion is large in comparison with a bottom portion. Therefore, a void is easily formed within the trench by blocking the opening portion. It is possible to restrain that the trench opening portion is previously blocked by simultaneously flowing a silane system gas and an etching gas (e.g., disclosed in JP-A-2004-273742).
However, a step difference caused by the trench is formed after a trench filling epitaxial process. Therefore, it is necessary to perform epitaxial growth for flattening and perform polishing.
Further, it is proposed that it is possible to prevent an opening portion of a trench from being earlier blocked by using a mixing growing system of an etching gas and a silane system gas with respect to the trench etched in a halide gas atmosphere in forming a p/n column structure by trench filling epitaxial growth.
Thus, the blocking of the trench opening portion can be restrained by an action of the etching gas, but a reduction of a growth rate is caused. Accordingly, a technique for improving the growth rate independently of the restraint of the blocking of the above trench opening portion is required.